This invention relates to a power source for gas discharge lamps and other loads operated at high frequency, and in particular is directed to a new and improved power source suitable for energizing fluorescent lamps and having a reduced peak ac line current. The present circuit is an improvement on those shown in U.S. Pat. Nos. 3,396,307 and 3,889,153, and those shown in copending applications Ser. No. 530,384, filed Dec. 6, 1974, now abandoned, and Ser. No. 596,069, filed July 15, 1975, and assigned to the same assignee as the present application.
The power source of the present invention has an inverter and a ballast circuit similar to those of the prior art devices. The prior art devices typically include a transistor oscillator circuit and a transformer, with a dc input voltage provided by an ac rectifier and filter circuit. The invention of the present application will be described herein as utilized with the power source of the aforesaid copending application Ser. No. 596,069, but it should be understood that the invention may also be used with other inverter power sources.
Inverter circuits have been improved so that some will operate over a wide range of dc supply voltages, thereby permitting the power supply filtering capacitor to be reduced to a very small value. The ac line current for the prior art power sources will have a triangular wave form, such as is shown in FIG. 3a and in one prior art circuit with a filtered capacitor in the order of 40 microfarads, the peak amplitude of the ac line is about 3 amperes. This triangular wave form results from the variable impendance loading of the inverter on the ac supply.
This relatively high peak primary ac current required by the prior art power source is sometimes undesirable because of the adverse effect on the requirements for the electrical distribution system in a building or an area utilizing the power source, especially when a large number of the power sources are utilized such as for the lighting of a large building.
It is an object of the present invention to provide a new and improved power source which will have the desirable operating characteristics of the prior art power sources while reducing the peak primary ac current requirements and thereby smoothing the ac loading on the distribution system.